WASHINGTON — With Russia pushing new hostilities to Europe’s doorstep, U.S. and NATO officials are trying to gauge whether already dwindling resources and attention will be diverted from what, until now, has been a top security priority: Afghanistan.

NATO, the international military alliance, is intent on continuing its 12-year mission in Afghanistan and has urged the government in Kabul to sign a security agreement allowing foreign troops to stay and train local forces beyond a Dec. 31 withdrawal deadline.

But with NATO states in Eastern Europe openly worried over Russian aggression, especially after Moscow this week annexed the strategic Crimean Peninsula from Ukraine, the alliance may have little choice but to bolster its own borders at some cost of keeping a robust and diverse military presence a continent away.

NATO Secretary-General Anders Fogh Rasmussen insisted Wednesday that Russia’s aggressions would not distract the military alliance from Afghanistan.

“We have the capacity to deal with several missions and operations at one and the same time,” Rasmussen said under questioning at the Brookings Institution think tank in Washington. “And ongoing events will not have any impact on our engagement in Afghanistan.”

Other experts said it is inevitable that some European nations — particularly those within Russia’s reach — refocus on securing their home fronts.

“Because the Europeans are more concerned about Russia as a threat, they will be less inclined to divert very precious resources to overseas-type missions, of which Afghanistan is clearly one,” retired Navy Adm. James G. Stavridis, the former NATO supreme allied commander and top U.S. commander in Europe, said in an interview this week.

“In resources for these smaller nations, they’ll want to put more attention and more focus on the very defensive level of effort,” said Stavridis, now dean of the Fletcher School of Law and Diplomacy at Tufts University in Medford, Mass.

The war in Afghanistan has been winding down over the past year, and the vast majority of the 52,000 troops from 49 nations who are there currently already are planning to head home.

It hasn’t been decided how many may stay, in large part because Afghan President Hamid Karzai has refused to sign a security agreement with the U.S. and NATO that would allow foreign forces to remain beyond December, when a United Nations mandate that authorizes their mission expires. Officials assume, and hope, that Afghan elections next month will yield a new leader who will agree to the continued military aid.

If permitted, it’s believed that as many as 10,000 U.S. troops and an additional 5,000 NATO forces will make up the foreign training mission in Afghanistan after 2014. Generally, NATO officials want to deploy forces from as many member nations as possible to demonstrate widespread support for the effort.

Excluding U.S. forces, NATO nations currently provide about 15,800 troops in Afghanistan, according to a Feb. 20 tally on its website. Of those, nearly 20 percent come from eight states that for years were under Moscow’s influence: the Czech Republic, Estonia, Hungary, Latvia, Lithuania, Poland, Romania and Slovakia.

Worried over Russian’s new advances, Poland and Latvia agreed recently to begin coordinating security activities more closely. And on Tuesday, Estonian President Toomas Ilves spoke of the end of what he described as a 20-year NATO philosophy of “out of the area or out of business” that assumed Europe no longer faced external threats.

“That unfortunately has turned out, with the actions we’ve seen against Ukraine, no longer to apply,” Ilves said after a meeting in Warsaw with Vice President Joe Biden.

Ukraine, which is not a NATO member, only had a few dozen troops still in Afghanistan as of Feb. 20, when unrest in its capital Kiev peaked, resulting in the ouster of its pro-Russian president. Leaders in Ukraine’s new government have sought inclusion in the European Union to ease domestic economic woes, but Prime Minister Arseniy Yatsenyuk said this week that Kiev has shelved its aspirations to join NATO to appease its pro-Russian citizens who oppose it.

The former Soviet state of Georgia also has been seeking NATO membership for years, and has more than 800 troops in Afghanistan. Stavridis predicted that Georgia will not step back from Afghanistan as it strives to show NATO and the U.S. it would be a reliable partner.

In turn, Washington is trying to reassure NATO allies that the U.S. will help defend them if necessary. So far, the U.S. has sent about 300 air troops and a dozen F-16 fighters to Poland for joint training and is considering rotating American forces to the Baltic region as a step toward shoring up NATO defenses.

But the U.S. is facing a military resources crunch of its own. Although the Pentagon has budgeted a $79 billion “placeholder” sum for 2015 operations in Afghanistan, it also is preparing to shrink its armed forces and is considering cuts to the two remaining Army brigades stationed in Germany.

Stephen Biddle, a security and defense expert at the Council on Foreign Relations, said it’s generally more expensive to keep troops in Afghanistan than it is in the U.S. or even Europe. He said a combination of budget pressures and nervousness over Russia could lead to further U.S. troop reductions in Afghanistan.

In the long term, the crisis could result in U.S. troops and military assets from around the world, including Afghanistan, being moved to Europe, said Christopher S. Chivvis, a European security and NATO expert with the RAND Corp. think tank.

“If you look further down the road, the big question is, What is the impact of this crisis going to be on the trajectory of the U.S. defense posture in Europe, which has been downward over the course of the last 20 years?” Chivvis said. “Before this, it was likely to continue on a downward path. So the question is now whether or not this crisis will stop that decline, or even potentially reverse it.”

Rasmussen, while maintaining a future military commitment in Afghanistan, nonetheless predicted the West will “need to take tough decisions” to preserve European security in light of Russia’s advances. He called the crisis in Crimea “the gravest threat to European security and stability since the end of the Cold War,” and cited fears that Russian President Vladimir Putin will push farther West to sow instability and prevent other former communist states from joining European alliances.

“My major concern is that this won’t stop,” Rasmussen told a crowded audience at Brookings.